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Your cat's nutrition is important for a healthy & happy life. petMD experts help you to know what to feed your cat, how much food to feed, and the differences in cat foods, so your cat gets optimum nutrition.

Nutrition Nuggets is the newest offshoot of petMD's Cat Nutrition Center. Each week Dr. Coates will use her expertise and wisdom to blog about the intricacies of cat nutrition.

Is There Enough Protein in Your Cat's Food?

We’ve spoken many times about the importance of including adequate amounts of protein in a cat’s diet, but all protein is not created equal. Unfortunately, it can be difficult for owners to determine whether the percent protein that appears on a food’s guaranteed analysis will actually meet their cat’s needs.

The crude protein percentage of a food is measured through a type of chemical analysis that determines its nitrogen content, which is based on the fact that proteins are made up of amino acids and amino acids contain nitrogen. This is the reason why unscrupulous producers have added melamine to food products (e.g., Chinese infant milk formulas and protein supplements added to pet foods). Melamine contains a lot of nitrogen (its chemical formula is C3H6N6 for anyone who’s interested) and can therefore “trick” the analysis into reporting a falsely elevated protein percentage.

But I digress. What I really wanted to talk about is the quality of the protein included in a cat’s food. Absent adulterants like melamine, the protein percentage listed in the guaranteed analysis contains proteins from both animal and plant sources. The chemical analysis used to come up with that number can’t differentiate between the two.

Cats are obligate carnivores. Since their natural diets consist almost entirely of other animals, they have a unique dietary need for specific types of amino acids (called essential amino acids) that they can’t make on their own. The system makes sense. Why waste your body’s precious resources manufacturing these amino acids from scratch when they are readily available in your food?

But some commercially available cat foods rely heavily on plant-based sources of protein. Plants can be a good source of protein in general but not the specific mix of amino acids that cats need to thrive. Therefore, these cat foods appear to be high protein based on the guaranteed analysis, but they cannot deliver an optimal amino acid profile without supplementation. Look at cat food labels and pick foods with meat or meat meals high up on the ingredient list.

Another limitation of the guaranteed analysis is that it does not provide any information about the digestibility of the protein in the food. For example, shoe leather contains a lot of protein, but while including it in a cat food might raise the percent protein on the guaranteed analysis, it won’t provide much protein to the cat. I suspect most would simply pass right through the gastrointestinal tract.

Labels aren’t a big help in determining how digestible protein sources are, so I use a cat’s response to the diet as a gauge of digestibility. If after a few weeks of eating the food, a cat is producing a “normal” amount of firm stool (not large quantities of loose feces that may contain mucus) and he or she has that unmistakable glow of good health, you’ve probably found a food that contains a good amount of digestible protein.

Actually, corn gluten meal has been shown to contain as much total amino acid content as most prey cats catch in the wild: http://www.ingredients101.com/cgm.htm The amino acid balance is very similar, except for the fact that leucine, that promotes muscle growth rather than fat is much higher in the corn gluten meal: http://www.ingredients101.com/cgm.htm

I have no problem seeing corn gluten meal as a SECONDARY source of protein in pet foods, and also prefer to see the meat source as "meal" because our pets are sedentary, altered house pets, not wild animals. The "gluten" in corn is not the same as the gluten content of ingredients that cause distress for celiac patients. I would not want other grain "glutens" in our pets foods.

JENNIFER COATES, DVM

... graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999. In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado. She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms, Vet-Speak Deciphered for the Non-Veterinarian .

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics. Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.